Method and arrangement for eye pressure measurements

ABSTRACT

An intraocular pressure measurement arrangement is disclosed for measuring pressure of an eye of a patient. The arrangement can include at least one source for producing mechanical waves of several frequencies from a distance to the eye of the patient to generate at least one surface wave to the eye, a detector for detecting at least one surface wave from a distance from the eye to extract surface wave information, and a device for determining pressure information of the eye based on the surface wave information.

RELATED APPLICATION

This application claims priority as a continuation application under 35U.S.C. § 120 to PCT/FI2015/050133, which was filed as an InternationalApplication on Mar. 3, 2015 designating the U.S., and which claimspriority to Finnish Application 20145205 filed in Finland on Mar. 4,2014. The entire contents of these applications are hereby incorporatedby reference in their entireties.

FIELD

Intraocular pressure (IOP) plays a major role in the pathogenesis ofopen angle glaucoma, a leading cause of blindness. There are about 150million people with glaucoma globally, about half of which areunknowingly affected and without diagnosis. The prevalence of glaucomaincreases with aging of the human population and it is expected thatthis will increase by 30% the number of glaucoma cases during the nextdecade. The only way to currently treat glaucoma is by lowering theintraocular pressure (IOP).

An IOP measurement is the most practical way of screening open angleglaucoma. However, screening large parts of the population is needed tofind undiagnosed cases.

The other type of glaucoma is the narrow angle glaucoma that causes asudden IOP increase that may cause blindness in a few days. Since oneper mile of the population is affected with acute narrow angle closureglaucoma, it is mandatory to diagnose acute glaucoma by measuring IOP incommunity emergency departments of general medicine. Consequently itwould be beneficial if every doctor's of would have the ability tomeasure IOP.

BACKGROUND INFORMATION

Contact methods (e.g. Goldmann tonometry, Mackay-Marg tonometry) formeasuring IOP mostly use an anesthetic to carry out the measurement andare thus impractical to, for example, screen large human populations.

U.S. Patent Application Publication No. 2010/0249569 A1 presents anon-contact ultrasonic tonometer for IOP measurements, which employspiezo-electric transducers to excite wave signals into the eye. Thepositions of the transducers have to be exactly measured, which makesthe IOP measurement procedure complex and slow. Also temperaturevariations cause error and uncertainty in the IOP measurementinformation together with possible errors in position measurements. Theshape of the eye also introduces bias (=error) into the measurement.

U.S. Pat. No. 6,030,343 presents a method that is based on an airborneultrasonic beam that is reflected from the cornea—the same beam measuresand actuates the eye. The actuation is done by a narrow band ultrasonictone burst, which deforms the cornea, and the system measures the phaseshift from the deformed eye.

Known solutions do not achieve a convenient and low-cost device formeasuring IOP precisely and comfortably for the patient by non-contactmeasurements.

SUMMARY

An intraocular pressure measurement arrangement is disclosed formeasuring pressure of an eye of a patient, wherein the arrangementcomprises: at least one source for producing an acoustic or a mechanicalwave from a distance coupling to an eye of a patient to produce surfacewaves of several frequencies by utilizing at least one of a patientheartbeat and breathing; means for detecting at least one surface wavefrom a distance from an eye to extract surface wave information; andmeans for determining pressure information of an eye based on saidsurface wave information.

An intraocular pressure measurement method is also disclosed formeasuring pressure of an eye of a patient, wherein the method comprises:producing an acoustic or a mechanical wave from a distance coupling tothe eye of the patient to produce surface waves of several frequenciesby utilizing at least one of a patient heartbeat and breathing;detecting at least one surface wave from a distance from the eye toextract surface wave information; and determining pressure informationof the eye based on said surface wave information.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present disclosure will becomeapparent to those skilled in the art upon reading the detaileddescription of the embodiments in conjunction with the accompanyingdrawings, wherein:

FIG. 1 presents a first exemplary embodiment according to the presentdisclosure;

FIG. 2 presents second exemplary embodiment according to the presentdisclosure; and

FIG. 3 presents another exemplary embodiment according to the presentdisclosure.

DETAILED DESCRIPTION

A contactless, fast and advanced device and method are disclosed tomeasure IOP without need for anaesthetics. An IOP reading that is bothprecise (i.e., unbiased) and features small uncertainty in the IOPestimate can be realized. This is achieved by an IOP measurementarrangement for measuring the pressure in an eye of a patient. Thearrangement can include at least one source for producing mechanicalwaves of several frequencies from a distance to the eye of the patientto generate at least one surface wave to the eye, means for detecting atleast one surface wave from a distance from the eye to extract surfacewave information, and means to determine pressure information of the eyebased on said surface wave information.

An intraocular pressure measurement method is disclosed for measuringpressure in an eye of a patient. The method produces mechanical waves ofseveral frequencies from a distance to the eye of the patient togenerate at least one surface wave to the eye, detects at least onesurface wave from a distance from the eye to extract surface waveinformation, and determines pressure information of the eye based onsaid surface wave information.

Mechanical waves of several frequencies can be sent from a distancethrough air to the eye of the patient to generate at least one surfacewave to the eye. At least one surface wave from a distance from the eyecan be detected to form surface wave information for determination ofpressure information of the eye.

Exemplary embodiments enable patient and user friendly use with no needto touch sensitive surfaces of an eye, together with advanced methods toprocess measurement information in order to extract qualified pressureinformation of the eye. One benefit is that exemplary embodiments can beutilized from one patient to another with less risk for contamination ascontact to the eye is avoided.

Essentially, excitation and/or detection of electromagnetic waves can beperformed by means of a beam of electromagnetic waves produced forexample, by a laser, pulsed laser or a plasma source (focused laser or aspark gap), which is for example mediated via an electromagneticwaveguide (e.g., an optical fiber, collimator, lenses, masks and/or anarrangement of mirrors) and targeted onto the eye of a patient or onto aspot in the vicinity of the patient's eye. An input of theelectromagnetic wave into or onto the eye is followed byelectromagnetic-mechanical conversion (e.g., photo-acoustic conversion)that generates little heat and significant mechanical vibration into theeye's tissues or a plasma source that launches sound waves that impingeon the eye to create a wave in it. Correspondingly, mechanicalvibrations of the eye tissue are detected (e.g., by means performingoptical interferometry, optical coherence tomography, laser Dopplervibrometry or by an ultrasound transducer). Exemplary embodiments cangenerate a mechanical wave or waves (e.g. ultrasonic waves) in the eyeand detect the waves in the eye. The potential applications relateespecially to determination of IOP; i.e., an eye pressure.

In exemplary embodiments non-contacting photoacoustic and ultrasonicintraocular pressure (IOP) measurement techniques can include thefollowing exemplary requirements: non-contact excitation and detectionmethods, which are safe for the patient, determination of essentiallyaccurate intraocular pressure (IOP) values, possibility to providefollow-up of patient's IOP values, and these techniques can be used by ahealth care professional and/or by a patient in a convenient andergonomic way with lowered risk for contamination from patient topatient.

There are several physical interactions that could be exploited for theIOP measurement. These interactions will be explained in order toevaluate their usability for a non-contact ultrasonic IOP measurement:

A) Physical systems such as the eye may vibrate at certain resonancefrequencies when they are mechanically or photo-acoustically disturbed.These frequencies depend on the mechanical properties of the componentsof the eye, and on the IOP as well as on eye size and shape as well asproperties of the eye socket. Measurement of the resonance frequenciescan be rather easy to implement, and preliminary data can be utilized tosupport the viability of the resonance measurements. Guided waves, suchas Lamb waves or quasi-Lamb waves or membrane waves that propagate oncurved structures can also be used in the measurements.

B) Lamb waves are guided waves that travel along a structure. They aredispersive; i.e., the phase velocity of a Lamb wave depends on thefrequency of the wave. Thus, with a single broadband excitation one canmeasure the dispersion relation of the waves, which is closely relatedto both the elasticity of the structure and stress caused by externalpressure such as for example the IOP. Broadband dispersion measurementsprovide more accurate IOP estimates than narrow band measurements.Several independent measurements can be performed on different parts ofthe eye, which can increase accuracy and decrease the confounding effectof the elasticity of for example, the cornea of the eye as well as theeffect of the eye socket. Preliminary data support the viability of theproposed method. Localized testing along lines can be performed, whichcould allow spatial averaging and could provide localized data as wellas anisotropy data.

C) Bulk wave velocities; i.e., longitudinal and shear ultrasonic wavevelocities, probe mechanical properties of measured materials. Thepropagation velocity of the longitudinal wave depends on the staticpressure loading the material (e.g. liquid) in which it propagates, andthe phenomena can be utilized to determine for example, IOP. Bulk wavesare simple to generate and measure, but for accurate (e.g., IOP)measurements, other measurements than bulk wave measurements are needed,because bulk wave measurements itself are unlikely to achieve highaccuracy.

D) Ultrasonic waves, both Lamb and bulk waves, loose energy as afunction of propagation distance. This energy loss decreases as afunction of pressure for bulk waves, but in loaded plates (e.g., theeye) due to the loading on the surface by the IOP, the effect isreversed. Quantitative measurements can be performed to calibrate theeffects of external pressure on Lamb wave attenuation. Attenuationanalysis is likely to be useful when combined with other properties(e.g., speed of sound, dispersion).

FIG. 1 presents a first exemplary embodiment according to the presentdisclosure, in which a spark gap 210 is placed near but not in contactwith the sclera of the eye 202. The spark generates a wave that uponcontacting the sclera launches two kinds of vibrations: first, elasticwaves (Lamb S₀ and A₀ guided ultrasonic modes), followed by a resonantvibration of the sclera and the cornea. The vibration can be picked upwith a custom made one-point interferometer 212 capable of detecting thetime-of-arrival of the wave. The mode map (i.e., frequency-velocitychart of Lamb waves traveling along the sclera) depends on theintra-ocular pressure (IOP). Also resonant frequencies depend on IOP.This kind of embodiment is affordable and simple to produce and allowsadding detectors to increase the measurement accuracy. Also a highsignal-to-noise ratio can be achieved by this kind of implementation.

The spark gap 210 produces a bright flash of light that might harm theeye 202. This can be avoided with a thin black membrane not in contactwith the eye. The membrane passes the acoustic pressure wave and blocksthe light from reaching the eye. The weak mechanical nonlinear wavegenerated by the spark can be audible and does not inducetissue-breaking stress. The intensity of the emitted wave can becontrolled to ensure that there is no risk to the hearing. Also thedetectors can use very low power lasers (even Class 1) in order tointroduce no safety risks to the eye.

The first exemplary embodiment can be improved by incorporating a custommade one-point interferometer capable of measuring vibration as afunction of time. This increases costs, but allows simultaneousmeasurement of both the resonance and the traveling Lamb waves, thusyielding more accurate IOP measurement information.

FIG. 2 presents a second exemplary embodiment according to the presentdisclosure, in which a pulsed (e.g., KrF excimer) laser 210 (e.g. 248nm) is used to excite mechanical wave(s) with a detection (e.g., a laserDoppler vibrometer (LDV) as detecting means 212). The excimer laser canbe focused on either the sclera or the cornea of the eye 202 or close tothem both, launching Lamb waves to the eye which are detected by adetection system 212 (e.g., the LDV). Several parameters canconcurrently be detected and correlated and calibrated to IOP: speed ofsound, attenuation, vibration spectrum of the received signal, detectedresonance frequency, etc.

UV wavelengths (or 1300-1550 nm IR (infrared)) absorb strongly into thecornea, and are thus unlikely to traverse the sclera. Interferometersuse generally a Class 1 beam, which is safe to the eye. The generatedLamb waves do not cause discomfort or damage. For example, the 248 nmwavelength absorbs extremely well into both the cornea and the sclera,thus not damaging eye structures beneath them. Benefits of such anembodiment are also low intensity values which causes no discomfort tothe patient and high absorption coefficient which improves signal tonoise ratio and hence both precision and accuracy of the IOP estimate.Also phase-delayed laser diodes can be used to shape the spectrum of thetransmit signal to increase the signal to noise ratio in the four modesin the mode map that is analyzed.

In first and second exemplary embodiments according to the presentdisclosure photoacoustic IOP measurements based on Lamb wave velocitydispersion and resonant frequencies of the eye/sclera are accomplished.A bi-modality embodiment (i.e. concurrent use of Lamb wave measurementsand resonance measurements) can be accomplished for example, by fourdetection points to pick up the wave excited in the middle to allow foursimultaneous and independent measurements. This provides precision. Thesensor 212 can also include ultrasonic transducers coupled to air whichto serve as distance and tilt measurement devices. An IOP measurementdevice (e.g. FIG. 3) according to the present disclosure can, forexample, include a spark gap 210 in the middle of the device, detectionmeans to pick up the excited waves from four points around an excitationpoint on the surface of the eye 210 and a built-in ultrasonic sensor 220detecting the distance of the device from the eye and the tilt of thedevice. The device can include direction lights or a display unit toindicate into which direction it should be tilted. This makes it moreoperator friendly.

FIG. 3 presents a first exemplary intraocular pressure (IOP) measurementarrangement according to the present disclosure for measuring thepressure in an eye 202 of a patient. The arrangement includes at leastone source 210 for producing mechanical waves of several frequenciesfrom a distance 200 through air to the eye 202 of the patient. The wavesgenerate at least one surface wave to the eye, and more specifically toa certain surface area of the eye and near the surface area of the eye.The embodiment can enable probing a certain site of the eye if one wantsto and even a certain direction along the eye ball. The surface wavescan include modes (e.g., Lamb S₀ and A₀ guided ultrasonic modes), andalso resonant vibrations that are generated to the eye. The source 210is for example, a spark gap 210 that generates by at least one spark anacoustic nonlinear wave (e.g., shock wave) that couples to the eye 202through the air and generates for example, both Lamb waves and resonantvibrations to the surface of the eye 202 and into the eye 202. Thesurface wave or waves are detected by means 212 for detecting from adistance 201 from the eye 202 to form surface wave information. Resonantvibrations can be detected by means 212 for detecting from a distance201 from the eye 202 to form resonance information. Detection of thepropagating Lamb waves can for example, be based on the time-of-arrivalof the first arriving signal (FAS), whereas the detection of theresonances can for example, be based on the Fourier transform of themeasured signal.

As will be apparent to those skilled in the art, the mechanicalnonlinear wave can also be generated by a mechanical impact of acombination of two hard surfaces or corners or edges (210) as the source(210) for producing nonlinear acoustic or mechanical waves, such asshock waves, of several frequencies from a distance (200) the wavescoupling to the eye (202) of the patient. For example, it is known thata hammer strike can produce nonlinear wide spectrum acoustic signalincluding ultrasonic frequencies.

The distance 200 or the distance 201, or both of them, can be optimizedby means 220 for controlling distance. The means 220 can be implementedfor example by ultrasonic transducers coupled to air for distance ortilt measurements and aiding the operator to position the device. Alsoaccelerometers or gyroscopes can be used to detect the best position andtime moment for the measurements. The means 220 for controlling andsetting an optimized distance 200, 201 from the source 210 and from themeans 212 to the surface of the eye 202 can also be implemented by anembodiment, in which the means 220 includes at least one laser emittingvisible light, and at least two (e.g., light) guides having first endsand second ends, the first ends connected to the laser for receivingvisible light. The means 220 can also include positioning means formoving the source 210 for producing mechanical waves or the detectingmeans 212 into different points (e.g. along a predetermined path). Eachof the second ends provides a light beam, and these light beams aredirected towards a surface of the eye 202 with an angle of convergenceK. The light beams are adjusted to intersect in a predetermined focuspoint, which is visible on the surface of the eye and which indicatesthe proper position and distance 200, 201 from the source 210 and fromthe means 212 to the surface of the eye 202.

The arrangement in FIG. 3 also includes means 216 for determiningpressure information of the eye based on the surface wave informationand for example based also on the resonance information. The means 216can be implemented by for example a processor unit in an IOP measurementdevice or by a separate computer unit to which measurement informationis sent from the IOP measurement unit via a wireless or wired connectionlink. The means 212 for detecting can be implemented for example bymeans of optical interferometry (i.e., by an optical interferometer), bymeans of optical coherence tomography (i.e., by an optical coherencetomography device), or by means of laser Doppler vibrometry (i.e. by alaser Doppler vibrometer), or by ultrasonic measurements using at leastone ultrasonic transducer, or with a combination of the differenttechniques. In a first exemplary arrangement the means 212 for detectingat least one surface wave includes at least one interferometer 212,which can measure the vibrations as a function of time, and which allowssimultaneous measurement of both the resonance vibrations and of thesurface waves (i.e., the Lamb waves), thus yielding a precise andaccurate estimate of the pressure of the eye 202. Exemplary embodimentscan use one inexpensive single point interferometer or more of them todetect time of arrival.

There can be either at least two wave sources 210 or detecting means212, or at least two of both, to improve measurement accuracy in formingthe surface wave information and the resonance information. In anexemplary arrangement of FIG. 3 the detecting means 212 are in threedifferent detection locations in order to improve measurement accuracyand precision and to obtain higher signal-to-noise ratio.

Heartbeat, eye blinking, and respiration cause temporal fluctuations inintraocular pressure. Of these, the heartbeat causes relatively constantpulsatile peaks in IOP, normally between 2-3 mmHg. This difference iscalled ocular pulse amplitude. This amplitude depends on heart rate andaxial length and there is a positive linear correlation between ocularpulse amplitude and IOP. High IOP causes high ocular pulse amplitude.Several other parameters, including ocular rigidity affects themagnitude of the ocular pulse amplitude. These pressure peaks causevibrations and waves along the eyeball (sclera and cornea) and alsointernally (e.g., iris), and the waves and vibrations can be detected(e.g. optically). An exemplary device according to the presentdisclosure can be used to measure, monitor, and analyze these heart beatinduced changes in the vibrations and waves to estimate IOP also withoutexternal stimulus.

Embodiments according to the present disclosure can improve comfort,accuracy, and precision of the IOP measurement by utilizing at least oneof the following features: 1) employing non-contacting measurement(comfort), 2) employing a localized and directional measurement (reduceseye shape-induced bias (error) to improve accuracy), 3) employing a slowwave form (symmetric & asymmetric Lamb waves, which reduces theconfidence limits of the sound velocity estimate=improves the precisionof the elasticity estimate=improves the precision of the IOP estimate,4) employing a broadband signal which allows mapping several propagatingmodes to gain precision in the sound velocity estimate (improvesprecision and potentially accuracy of the tester) 5) employing ageometric transmit and receive array or phased array (improved SNR whichreduces the confidence limits of the sound velocity estimate due tolarger signals and due to ability to fit the estimate with a regressionline, this improves precision), 6) the array approach also allows tuningthe modes to be employed for improved SNR and consequently precision andaccuracy of the tester/test, 7) employing both the travelling waveapproach described above and the known resonance concept. Since thesemeasurements are independent of each other a more sensitive and robusttester follows (it should improve both precision and accuracy). Themeasurement can be generalized to other physical parameters such assound attenuation (absorption, scattering) and sound velocitydispersion.

In an exemplary embodiment according to the present disclosure, patientheartbeat or breathing or both of them is used as a source for producingsurface waves of several frequencies detectable by means 212 from adistance 201 to the eye 202 of the patient. In another embodimentaccording to the present disclosure, means 210 to generate tiny plasmaburst is used as the source 210 for producing acoustic waves of severalfrequencies from a distance 200 to the eye 202 of the patient. Thegeneration can be made by sparking or by focusing a laser ray to onepoint on the surface of the eye or close to the surface of the eye. Inan exemplary embodiment according to the present disclosure, means 210to generate chemical reaction is used as the source 210 for producingacoustic waves of several frequencies from a distance 200 to the eye 202of the patient.

In further exemplary embodiments according to the present disclosure,mode tuning is used by phase delayed excitation in source 210 forproducing mechanical waves of several frequencies from a distance 200through air to the eye 202 of the patient. An improved signal to noiseratio (SNR) and improved time of flight (TOF) estimate can be achievedby mode tuning performed on the basis of phase delayed excitation.Precision and accuracy of TOP measurements according to the presentdisclosure can thus be increased.

Also, in exemplary embodiment according to the present disclosure, aphotoacoustic laser-based excitation can be performed by having a ringshaped form to the surface of the eye or close to that surface in orderto amplify the surface wave in the middle of the ring shape. Thisenables easier and more accurate detection to be performed by thedetection means. It also permits a cheaper receiver to be used. The usercan combine the use of a shaped (i.e., circle or line or crescent)source with the phased array concept having many dots, lines orcrescents for improved precision and accuracy in the IOP measurement.

On the basis of the present disclosure an ideal tonometer can beimplemented which is capable of measuring intraocular pressure with fastcomfortable measurements without anesthetic and disposable waste, and ofoperation by an unskilled operator.

Although the invention has been presented in reference to the attachedfigures and specification, the invention is not so limited. It will beappreciated by those skilled in the art that be appreciated by thoseskilled in the art that the present invention can be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. The presently disclosed embodiments aretherefore considered in all respects to be illustrative and notrestricted. The scope of the invention is indicated by the appendedclaims rather than the foregoing description and all changes that comewithin the meaning and range and equivalence thereof are intended to beembraced therein.

The invention claimed is:
 1. An intraocular pressure measurementarrangement for measuring pressure of an eye of a patient, wherein theeye includes a sclera and a cornea, the intraocular pressure measurementarrangement comprising: a contactless wave detector that is locatable ata detection distance from the eye, the wave detector being configured todetect at least one surface wave produced on the eye by at least one ofa patient heartbeat or breathing and containing plural wave componentshaving frequencies corresponding to at least one of patient heartbeatfrequencies and patient breathing frequencies, the at least one surfacewave being produced without stimulus provided by the intraocularpressure measurement arrangement, the wave detector being configured todetect a part of the at least one surface wave that contains the wavecomponents having the at least one of patient heart-beat frequencies andpatient breathing frequencies, and wherein the intraocular pressuremeasurement arrangement does not comprise any source for producingacoustic or mechanical waves from a distance to the eye of the patientto generate the at least one surface wave to the eye such that the wavedetector is configured to detect the part of the at least one surfacewave from a surface of the eye when the eye is open, the detected partof the at least one surface wave that contains the wave componentshaving the at least one of patient heartbeat frequencies and patientbreathing frequencies and containing surface wave information dependenton the ocular pressure of the eye; and an intraocular pressuremeasurement unit comprising a processor operatively connected to anoutput of the wave detector to receive the surface wave information, theintraocular pressure measurement unit for determining pressure of theeye based on said surface wave information dependent on the ocularpressure of the eye and providing the determined pressure of the eye asan output of the intraocular pressure measurement arrangement.
 2. Anintraocular pressure measurement arrangement according to claim 1,wherein the wave detector comprises at least one interferometerconfigured to measure vibrations as a function of time for the surfacewave that contains the wave components having the at least one ofpatient heartbeat frequencies and patient breathing frequencies.
 3. Anintraocular pressure measurement arrangement according to claim 1,wherein the wave detector is configured to detect the part of the atleast one surface wave that contains the wave components having the atleast one of patient heartbeat frequencies and patient breathingfrequencies at least in two different detection locations in order toimprove measurement accuracy and to obtain higher signal-to-noise ratio.4. An intraocular pressure measurement arrangement according to claim 1,wherein the wave detector comprises an optical interferometer configuredto detect and measure said wave components resulting from heartbeatand/or respiration and containing ocular pulse amplitude informationcorrelated to the intraocular pressure (TOP).